A high volume shock will not be as progressive as one with a standard can so yes, it will go through the end of the stroke faster/easier.

as the it has a regressive rate rear suspension design, & the HV shock with it linear action, means that their not well suited to each other (it'd bottom out easier).

I'd get your Float R tuned

it will still be progressive, just not as much. I'd stick with what the manufacturer chose.

Is the prophet actualy regressive or aproximately linear?

pfft I dunno I just read someone say it and someone say it about the heckler too. If it's linear I might get the high volume one as this float is about as plush as a girder.

The Prophet's regressive rate is designed with a low volume shock in mind so that the natural progression of the air shock works out as a linear rate on the bike. A high volume shock will just plunge through the travel in a less controlled way. If you can afford it, get a 2010 RP23 with the boost valve. Works superbly on my Prophet.

Consider getting the propedal tune changed on the float. Mine was like a completely different shock afterwards.

The prophet is definitely a falling /regressive rate frame design, so a high volume shock would be a bad idea - you'd almost certainly end up with a falling rate overall, which is rubbish (poor small bump sensitivity and easy bottoming).

I add extra oil to the air chamber on my standard size rp3 in order to reduce the volume a touch further and thus make the shock more progressive. This is to counter the falling rate design of my C'dale rush (which is very similar to the prophet).